Specifically designed as an alternative to Access and FileMaker, Kexi is a visual database application creator that allows non-programmers to make simple data-driven applications. It is part of the KDE project and the Calligra office productivity suite. Operating System: Windows, Linux, macOS

One of the most popular open source projects in existence, MySQL is used by many well-known websites, including Facebook, Google, Adobe and Zappos. In addition to the free Community edition, Oracle offers paid Standard, Enterprise and Cluster CGE editions. Operating System: Windows, Linux, Unix, macOS

Desktop Publishing

While not as full-featured as Scribus (see below) or the proprietary applications listed above, MiKTeX does one thing really well — it typesets scientific and mathematic text. It’s cross-platform and can even run from a portable thumb drive or other storage device. Operating System: Windows, Linux, macOS

Compiere offers a full-featured ERP solution with capabilities very similar to iDempiere (see below). It also comes in a paid cloud version that runs on Amazon Web Services. Operating System: Windows, Linux, macOS, others

Ideal for small businesses, freelancers and foundations, Dolibarr combines ERP and CRM functionality in an easy-to-use interface. The site also features a store where users can purchase hosting, addons and related services. Operating System: OS Independent

Claiming to be the "most powerful open source ERP," ERP5 counts banks, universities and corporations like Airbus among its users. It includes accounting, CRM, HR, project management, inventory, manufacturing, ecommerce, product data management, knowledge management, point of sale and many other capabilities. Operating System: OS Independent

The Compiere and Adempiere projects have been involved in a number of disputes over the years, resulting in forks and name changes. The current successor project to Adempiere is iDempiere, which includes ERP, CRM and supply chain management capabilities. Operating System: Windows, Linux, macOS, others

Used by companies like the World Wildlife Federation, Toyota and Hyundai, this comprehensive ERP solution includes modules for sales, ecommerce, accounting, point of sale, project management and inventory. In addition to the free Community edition, it also comes in Online and Enterprise editions, and the Online edition is free for fewer than 50 users. Operating System: Windows, Linux, macOS

Named a “cool vendor” for Spain and India by Gartner, Openbravo offers both paid and free open source ERP solutions. It can be difficult to find the community versions for download, but they are at code.openbravo.com. Operating System: OS Independent

Another Web-based option, weERP was designed specifically to meet the needs of wholesalers, distributers and manufacturers. There's an online demo on the site so you can give it a try before you download. Operating System: OS Independent

XTuple offers multiple ERP solutions, and PostBooks is the free, open source version that provides the core for the company's other products. It includes tools for managing sales, accounting, operations and CRM. Operating System: Windows, Linux, macOS

Firewall and Unified Threat Management

With Endian Firewall Community and an old PC, you can easily create a turn-key firewall for your home or small business network. It includes a stateful firewall, email security, intrusion prevention, network quality of service, VPN, antivirus, reporting and multi-WAN capabilities. The company also offers paid products based on the open source core. Operating System: Linux

Untangle offers similar functionality to Endian, with the option to install security apps individually so that you get exactly the functionality you want. The website includes both free and paid software for download, and pre-configured appliances are also available for purchase if you don't want to use your own hardware. Operating System: Windows, Linux